VISCOSITY AND FLUIDITY

fluidity curves are much more nearly linear than are the viscosit
curves, the true linear curve being represented in each case bv
series of dashes. Mercury is an ideal substance in this connec-
tion for it is far removed from the critical temperature, it is not
highly associated, and its volume increases in a linear manner
with the temperature.1 The fluidity curve is almost perfectly
linear, what curvature there is being in a direction opposite to
that of every other known substance, so that it can hardly t>e

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Temperature Centigrade.

36. — Fluidity (continuous) and viscosity (dotted) temperature curves for
mercury and water.

regarded as certain that this deviation is not due to experimental
error. An extensive study of the fluidity-temperature curves of
p-ure liquids leads to the conclusion that even when the expansion
Is not linear and there is association, the curves approach linearity,
as is seen to be the case with water in the figure. The extent to
which this is true can be best judged by an algebraic analysis
of the data to be given later. However it may be stated here
that the ffarst approximation of Meyer and Rosencranz (1877)

1 Landolt and Bernstein, Tabellen, 3d. ed., p. 41.